The background description provided herein is for the purpose of generally presenting the context of the disclosure. Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Magnetic storage systems such as hard disk drives are used to store data. The hard disk drives include one or more platters with an outer magnetic coating. The magnetic coating stores positive and negative magnetic fields that represent binary 1's and 0's. The platters are divided into concentric circles called tracks. The tracks are divided radially into sectors.
When the hard disk drives are manufactured, a servo writer writes permanent servo wedges onto the platters between the sectors. The servo wedges contain data that is used by a HDD to locate the tracks and data sectors. The information stored in SERVO wedge includes track ID and sector ID's that are coded using Gray code.
Gray code represents consecutive decimal numbers using binary expressions that differ by only one bit. For example, the decimal numbers 0 and 1 can be represented by the binary Gray code numbers 00 and 01, respectively. The decimal number 2 can be represented by the binary Gray code number 11. The decimal number 3 can be represented by the binary Gray code number 10.
Throughout the lifetime of a disk the servo data will be read repeatedly, with read noise varying from read to read. Gray code quality checks are performed to identify wedges that are error prone. Gray code quality may be reduced for a number of reasons including media defect, strong jitter noise realization, and the like.